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POTABLE WATERS

test with distilled water and to make allowance for any permanganate
consumed thereby.

2.   Complete Analysis

Complete analysis of a water includes, in addition to the determinations
of the partial analysis, the following estimations.

1. Dissolved Gases.—The gases usually found dissolved in water
are oxygen, nitrogen and carbon dioxide. They are measured by extract-
ing them from the water by means of a, pump or by boiling, collecting them
in a graduated vessel and measuring their total volume. The carbon dioxide
is then absorbed by caustic potash, and the oxygen by alkaline pyrogallol,
the nitrogen remaining.

The apparatus and methods used for estimating gases in water are many,
and detailed descriptions of them may be found in special treatises.1 One
of the simplest modes of procedure consists in using an ordinary nitrometer
(Fig. i).

The water to be examined is collected in a, tared half-litre; ilask, A,

which is filled completely and is then closed
with a perforated rubber stopper through
which passes a glass tube sealed at the
lower end and 'furnished with a lateral
orifice, the latter remaining within the
stopper during transport so that the flask
is kept hermetically sealed.

The full Ilask is weighed to give the
amount of water taken and is then arranged
on a gauze over a, burner and connected
with the nitrometer, />', by means of the
tube a. The nitrometer should be lilled
with previously boiled, saturated sodium
chloride solution, which is also used to fill
the small tube in the stopper of the Ilask
and the whole of the tube: a, so that no
bubble of air remains in the apparatus. By
means of a T~pieee inserted in the, tube a at
c, it is easy, by opening the clips at b and c to fill the whole with the salt
solution in the nitrometer.

When all is ready, the small tube is forced down until its lateral orifice
is below the stopper of the flask, the clip h is opened and the flask heated,
the liberated gases collecting in the nitrometer. During all this time the
bulb, C, of the nitrometer is kept down. When evolution of gas ceases,
the clip & is closed, the bulb C raised until the level of the liquid in it corro

1 For instance, Franklancl, Water Analysis (London, 1880); Tiemann untl Gaert-
ner, Die chemische wnd bahteriologische Untcrsuchimg den Wassers, 4th edit. (.Brunswick,
*%93) ; OhlmtUler, Die Untcrsuchung untl L'curtcihmg des Wassers und Abwassers :
Leitfaden fiir die Praxis und zwn Gebrauch im Laboratorium (1910); Peannuin and Moor,
The Chemical and Biological Analysis of Water (London, 1899); Lunge, Technical
Methods of Chemical Analysis (London, 1908). Fresenius, Quantitative Analysis;
Guareschi, Nuova enciclopedia di chimica, Vol. Ill (Turin, 1901).

FIG. I.acid solution, and titrated with the permanganate. The oxygen